A lawsuit filed in California by concert giant AXS has revealed a legal and technological battle between ticket scalpers and platforms like Ticketmaster and AXS, in which scalpers have figured out how to extract “untransferable” tickets from their accounts by generating entry barcodes on parallel infrastructure that the scalpers control and which can then be sold and transferred to customers.

By reverse-engineering how Ticketmaster and AXS actually make their electronic tickets, scalpers have essentially figured out how to regenerate specific, genuine tickets that they have legally purchased from scratch onto infrastructure that they control. In doing so, they are removing the anti-scalping restrictions put on the tickets by Ticketmaster and AXS.

In the lawsuit, AXS said brokers are delivering “counterfeit” tickets to “unsuspecting consumers,” and that they are “created, in whole or in part by one or more of the Defendants illicitly accessing and then mimicking, emulating, or copying tickets from the AXS Platform.” The lawsuit accuses these services of hacking and states that AXS does not know how they are doing it. But the tickets themselves are often not counterfeit at all, and in the vast majority of cases, they scan as genuine.

Two security researchers we spoke to reverse engineered how Ticketmaster generates ticket barcodes and showed how scalpers can generate genuine tickets for concerts themselves. The system that works for Ticketmaster is also likely to work for AXS tickets, which use similar “rotating barcodes” that change every few seconds. After one of the researchers published their findings in February, they were approached by brokers and were asked to build ticket transfer services for them.